1. Field of the Invention
The present invention relates to a method of manufacturing a solid electrolytic capacitor, and particularly relates to a method of manufacturing a solid electrolytic capacitor having a conductive polymer layer as a solid electrolyte.
2. Description of the Background Art
In recent years, accompanied with digitization and realization of high frequency of electronics, a small size and a large capacity and low impedance in a high frequency range are required for the electrolytic capacitor. Furthermore, accompanied with increase in a reflow temperature due to making solder free from lead, high heat resistance is required for the electrolytic capacitor.
A solid electrolytic capacitor having a wound-type capacitor element structure has been developed and made into a practical use in which a conductive polymer such as polypyrrole and polythiophene having high conductivity is used as a solid electrolyte for such requirements of small size, large capacity, and decrease in impedance in a high frequency range (for example, Japanese Patent Laying-Open No. 11-186110). The solid electrolytic capacitor having a wound-type capacitor element structure can be produced by storing a capacitor element having an anode foil and a cathode foil wound with a separator interposed therebetween in a metal case and sealing its opening part with a sealing rubber.
Presently, polyethylenedioxythiophene (PEDT) has been used often as the conductive polymer for reasons that it has high conductivity, polymerization reaction is gradual, and it has an excellent adhesiveness with an anode dielectric film.
A wound-type solid electrolytic capacitor having a PEDT layer as the solid electrolyte can be produced by impregnating 3,4-ethylenedioxythiophene which is a monomer and an oxidizing agent into a capacitor element having an anode foil and a cathode foil wound with a separator interposed therebetween and performing chemical oxidization polymerization. Ferric paratoluenesulfonate or the like is used as the oxidizing agent for example.
However, the above-described conventional solid electrolytic capacitor is not sufficiently satisfactory in the respect of heat resistance. That is, in a reflow process of the solid electrolytic capacitor with lead-free solder, because the lead-free solder has a considerably higher melting point than that of the conventional lead solder, there is a necessity of making the solder reflow temperature a high temperature of about 200 to 270° C. However, in the conventional solid electrolytic capacitor, deterioration of electronic characteristics accompanying with deterioration of the conductive polymer such as PEDT proceeds excessively, and it becomes a problem that cannot be overlooked in the market.